Recovery of alkali metal compounds



Patented June 9, 1931 UNITEDv STA Tl-:s PATENT .o1-*FICE CHARLES A.GRONDONA, OF SAN FRANCISCO, CALIFORNIA, ASSIGNOR T I .PROCESSES INC., 0FSAN CISCO, CALIFORNIA, A CORPORATION OF DELAWARE i RECOVERY or ALKALIMETAL' COMPOUNDS Application mea september 2s, 1927. serial Nb.222,593.y

This invention relates generally to meth- Y ods and apparatus foreffecting recovery of chemicals from yliquors and is particularlyadapted for the smelting of` concentrated black liquor to recover adesired salt of an alkali forming metal therefrom. v

'p In the manufacture of sulphate or kraft pulp, a substance commonlyknown as black liquor is obtained which is generally passed thru aconcentrating and smelting process for the recovery of valuablechemicals. The smelting process is often carried out in a spray typefurnace vinto Which the concentratedV black liquor is introduced bysuitable spray nozzles, injectors, jets, pelletizers, or other suitabledevices. With other types of furnaces, such as the black ash furnace,the black liquor is desiccated to the form of black ash to which isadded an amount of soo dium sulphate required in operationv ofthe pulpprocess and the mixture is then shoveled into thefurnace in solid form.The smelting operation is carried out by the4 partial destructive Ydistillation of the organic compounds in the blackliquor with thesubsequent combustion of the volatile substances formed thereby. Thesodium sulphate Vor sodium bisulphate is then reduced by the carfv bpn.of the black liquor to form `sodium sulphide, the necessary heat duringreduction being furnished by combustion of the carbon and unreducedorganic matter.` f

In the latter typenand infurnaces in vvhic the black liquor isintroduced in4 concentrated liquid form in such a manner as to support azone of combustion above thefurnace bed, the furnace must perform threeessential functions; first the Water must be removedfrom thel liquor byevaporation; second the combustible organic matter. (principally lignin)in the `black liquormust be burned, and third the sodium sulphate whichis 'introduced into the furnace must react at anr elevated temperaturewith carbon of the lignin toproduce sodium sulphide. y

Y In the past with thespraytyp'e Vof furnace it has beenthe practicetomix the salt'cake, or sodium sulphate, with the black liquor eitherbefore or while itis sprayed vinto the furnace. By this method it isattempted to secure an intimate contact between the salt cake and theblack li uor, and tol uniformly distribute the salt ca e inthe liquor.In carrying out this process the liquor and salt cake mixture is sprayedinto the furnace at ity of sprays are employed, they enter fromapproximately the same level. amount of reduction ofthe salt cake prob.-ably occurs While the Vparticles are in flight substantially thesamezone, and if a plural,-V

in the furnace, and some further reductiony takes place by the action ofthe salt cake with carbon produced from the organic matter and Whichfalls to the bottom of the furnace. A partial reduction of the sodiumsulphate to sodium'sulphide thereby takes place and a molten mixturecontaining principally carbonate, sulphide and sulphate of sodium isdischarged. In `all processes of this" kind which have been utilized inthe. past there is a substantial percentage of unreduced sodiumsulphate', Which represents a loss of chem` ical and thereby renders theVprocess inefficient. The black ash furnace gives asa rule a greaterconversion of thesulphate tosulphide, the sulphate present in the smeltbeing from 4 to 10% While with the spray type, itis difficult to keep itunder 16%.

` It has been attempted to reduce the percentage of unreduced sulphateby forming a reduction or smelting bed in thebottom of the furnace so asto kcepthe lsodium sulphate in contact with carbon under apreducingcondition. A reduction bed of this kind will materially increasetheefhciency `of suchl fur.-

naces if it can be successfully maintained un,

der proper condition of temperatureand air supply. However in priorprocesses it has. been practically impossible to maintain such areduction bed for the reasonthat the introduction of the concentratedblack liquor and the air supply have to be controlled primarily for thepurpose of-maintaining propercombustion, and the conditions whichVcontrolV bed. Thus ifin such prior processes the introductionof blackliquor is controlled so as A certain -combustion'are inconsistent Withthe factors VWhich control maintenance of the reduction to obtain propercombustion, the reduction bed will not be efiiciently maintained.V

It is an object of this invention to devise a process of smelting blackliquor which will reduce the percentage of unconverted sodium sulphate.y i Y It is a furthe-r object of this invention to devise'a'process ofoperating'a smelting furnace whereby a reduction bed may be effl- 10oien'tly maintained .at 'the bottom ofthe fur- Y nace underoptimumtemperature conditions.

' It isa furtherobject of this invention to improveupon the operation ofsmeltin-gf-fur- V-naces for black liquorby rendering the combustion morestable and by carrying out the processwith as much economy of heat aspossible.` Y i n Y .v Further objects of this invention will appear fromthe following description in which ZOI have set forth the .preferredembodiment of my invention. It islto be; understood that the appendedclaims are to b e accorded a rangeV of equivalents consistent with thestate of the prior art.'V

'Y The Single figure of the drawing shows a furnace capable offbeingutilizedwith the p'rocessof this'invention. y Y K Y Y the use of myinvention,7it is possible to regulate the introduction of black liquorinsuchva way as not only to securep-roper combustion but also toproperly maintain the reductionbed; This-is made-possible by separatelymaintaining two zones of combustionY within the furnace.' In theupperkpart of .'35 the furnace part of the black liquor is intro,-

duceld and the sprays or other devices used areso located, regulated andsupplied with air as to result vin complete dehydration andsubstantially complete combustion forming thereby a combustion zone'ofrelatively high temperature. Between this upper zone and the bedy ofthefurnace, I maintain anotherl zone ofcom-bustion by the introduction ofbothV the balance of the black liquor and the' sodii'im-sulphateat alower level Vthan the feed forthe upper zone. The'spraysor other devicesused are sovlocated, regulated and Y. supplied with a restricted amountof air that inthe lower zonethe water isvremoved from the black-liquorby;V evaporation, but partial combustion only of the material added atthis point takes place. 'l Such combustion as takes placein this zone ischiefly of the liberated volatile' combustible constituents andsuch'carbonmonoxide gas as is formed below.V The solid combustibleconstituents, cpm'prisi'ng'mainlyV ak spon'g'yA carbon which is mixedwith alkali residues` from black liquorandaddedsa'lt cake', are notcompletely y consumed.r` These? solids, V together with thealkaliresidues from thecombustion `in the Y upperfzone form a bedrofanydesired thick-`V ness-on the bottom of the furnace in which reducingconditionsV canjibe' readily maintained and the .reduction of vsulphateto sul-l f phide thoroughlyeffected. This reaction and the snielting ofthe mixture of sodium salts require an elevated temperature, (of thedegree of aboutl700 to 20000 E), which is maintained, in part byradiation'of heat from by the oxidationl of the carbon Vin the bed.VVThe relative quantity of'concentrated black Yliquor'introduced intheupperv and the lower zone must be foundby experiment for eachparticular furnace, theA optimum' condition u being that which givesgreatest Vfurnace casulphide. -The exact position of the zones` inany'furnace will' depend on the size and fpaeity-with -eincientreductionof sulphate to design of the furnace, ,the extent'to which n the blackliquor has lbeen concentrated, and the capacity of the furnace.

In the drawingv I have diagrammatically shown a furnace suitableforcarrying out the? processY of this. invention. `The in ner :com-kbustion chamber 10 of the furnace 1s preferably relatively highcomparedL to itsf'crossA seCtiOnalarea, preferably as muchas three orfour `times as high as its diameter. Concentrated blaclrliquor,ycontalningfiftyv Vperi centor more solid matter, is introducedinto theupper portion jlof the furnace thru suitable means such las a pneumaticspray*` noz,-

zle 11. Arranged at av diiferent. level with re- '95 spect tothe nozzle11,v there Y is additional means .suchv as a pneumatic nozzle 12' for.spraying additional black liquor into the low- Ver portion of thefurnace.,v The salt cake may belpremixed with the black liquorintroduced thru nozzle 12, or preferably is .separately in.

jected thru a suitable ypneumatic nozzlel, I

whichis adapted to receive cake from the hopper 14. y .v A

In operating the furnacedisclosed,` an `up' per zone ofgcombustionvl'i's maintainedby the burning of' concentrated black 'liquorintroduced-thru nozzle 11, and inthis zone 'substantially all of thevcombustiblel constituents" of the' blackfliquor vare consumed. 'Theinlpowdered'.l salt:

ios

tense radiant heat'- thrown. downwardly*Vv the zone ..16. tends todehydrate' and sustain partial combustion r of lthe-black liquor'introduced thru nozzle 12, thusforming aalower Y Vzone ofcomb'ustion 17,Thenon-combustible solid 4residues-*from the upper-zone 16 fall tothebottom of the furnace thru the lowerzone- 17 ,and together withtheunconsumed con-l Y stituents of the black liquor introduced into thezone 17 'and with thesaltcake-forni'athe furnace bottom: rEhetemperature of this bed ismaintainedat'fa value suiicientto car"-v4 ryout the 'reaction between .the carbon particles and' the-'salt cake, say. betweeny the tern-f` peratures of 1700 degrees to,v 2000l deg;Fabrik? 19, and bylmeans' ofjr'adiant heatA absorbed from `the uppercombustion fzones,vflhfefVK enheit'by furthercombustion offc'arbon par`v Y ticles by means of air 'introducedthru` tuyres `the upper zone ofthe furnace and in ,partV im i amount of air introduced thru nozzles 12and i 18, and thru the` tuyres 19 isV so restricted that completecombustion cannot takeeffect in the zone 17, and so that 'the carbon inthe bed 18 is not consumed until substantially all of the salt cake hasbeen converted thereby maintaining a reducing condition. As a result ofthe smelting action, a molten mixture consisting chiefly of carbonate,sulphide and sulphate of sodium is discharged from the bottom of thefurnace thru the opening 21. Gaseous products of combustion from thefurnace may be removed thru opening 22 connected to a stack or otherdraft means, and air to support combustion in the Zone 16 may beintroduced thru the opening 23, or by other suitable means.

In oner installation which I have completed and successfully operated,the furnace measured 7 feet inside diameter and the combustion chamberwas 2O feet in height. The black liquor for the upper combustion zonewas introduced about-5 feet from the top, of the furnace, and the liquorand sulphate for the lower zone was introduced about 9 feet from thetop. YA smelting bed of about 5 feet in thickness was maintained uponthefurnace bottom. The black liquor employed contained about solids andabout two-l thirds of the liquor was introduced into the upper zone andabout one-third into the lower zone. The combustion was exceedingly'stable and the percentage of unconverted sulphate ranged from 8 to 12%.In prior smelting furnaces using simple spray injection of black liquor,the unconverted` sodium sulphate ranges from 14 to 18%. Y

I claim:

1. In a method of recovery of a salt of an` maintained by the separateinjection of the black liquor into the upper part of the furnace.4

4. In a lmethod of recovery of a salt' of an falkali forming metal fromblack liquor having combustible constituents, the step comprisingseparately maintaining two combustion zones above the furnace bed byspraying said liquor into theV furnace, the .upper zone being of hightemperature and effecting substantially complete combustion of saidcombustible constituents, the lower zone beino' of lower temperature andeffecting partial combustion of said constituents whereby a reducingzone is maintained.

5. In a method of recovery 'of a salt of anV alkali forming metal fromliquor having combustible constituents, the steps comprising separatelymaintaining two combustion zones above the furnace bed by theintroduction of said liquor,rthe upper zone being of- Intestimonywhereof, I have hereunto set my hand.

. CHARLES A'. GRONDONA.

the introduction of black liquor, and introducing additional blackliquor Vand salt cake into the furnace between said zone and thev lowerportion of the furnace.

2. In a method of recovery of a salt of an alkali forming metal fromblack liquor, the step comprising maintaining a zone of oombustion inthe upper part of the furnace, the zone being independently maintainedwith respect to the lower portion of the furnace, and maintaining areduction bed in the lower portion of the furnace by spraying blackliquor and salt cake into the furnace between the bed and the upperindependently maintained Zone of combustion.

3. In a method of recovery of a salt of an alkali forming metal fromblack liquor, the steps comprising injecting black liquor into an upperpart of the furnace, and maintaining a reduction bed in the lowerportion of the furnace by spraying black liquor and salt cake into thefurnace between the furnace bed and an upper zone of combustion

